This invention relates to modular multiple-story buildings, intended for human occupancy, such as apartment buildings, hotels, schools, dormitories, offices and any buildings with a plurality of repetitive room sizes, where the prefabricated standard elements can be used.
Such buildings are usually characterized by regular floor patterns and arrangement of columns, extending through all stories, so a system of beams and girders on columns forms a multi-story skeleton frame which supports the outside walls, roof and floor elements or prefabricated box-like modules and resists all vertical and horizontal loads imposed upon the building. The lateral (wind or seismic) loads are usually assumed to act as a concentrated forces applied at the floor and roof levels and distributed to rigid or braced frames, shear walls or other vertical load-resisting elements providing building stability. Therefore, the floor and roof deck systems of a plurality of slabs and beams act between lateral supports like a beam, loaded in a horizontal plane (horizontal diaphragm). To properly perform the diaphragm function it is essential that the integrity of all prefabricated elements is accomplished. Such integrity can be attained by welding special mechanical connectors to steel inserts embedded in every precast concrete element. The commonly used reinforced concrete floor and roof precast slabs are narrow (flat, ribbed, waffle, hollow-core, single or double tees), and the numbers of the joints between them is significant. Due to the plurality of inserts, connectors and field welded welding spots, this method is expensive and protracted. More frequently, the cast-in-place floor-topping concrete with wire mesh reinforcement is used. This procedure has an inherently relatively high labor content during on-building-site assembly and additional spending of concrete and steel. By using prefabricated modules and beams, the horizontal load translation can be accomplished by the longitudinal beams.
The prior art includes building lateral supports which are either rigid or braced frames or walls constructed according to necessity which withstand all horizontal loads and provide vertical supports for floors. The braced frames use pin connections and vertical braces such as cross braces or K-braces to make a more rigid structure. The walls and braced frames are, of course, sometimes undesirable since they may interrupt the space which would desirably be left open. All rigid frames use moment connections which restrict turn between columns and girders and produce a rigid construction. The larger the building, the larger the girders, because wind loads on larger buildings are greater.
Joists may extend between the girders and plates may sit on the joists to sustain the required load. One of the most common types of floor construction is the slab-joist-girder system with a one-way slab. The dead and live load acting on such slabs are transferred in the short direction hence the main reinforcement is parallel to the short side of the slab and the deflected surface is primarily one of single curvature. If the slab is supported at least on three edges and the ratio of the long span to the short span is less than about two, the loads are transferred in both directions and the deflected surface becomes one of double curvature, the slab is defined as a two-way slab. In two-way concrete slabs the main reinforcement usually runs in two directions.
The required distance between lateral load-resisting supports depends on the intensity of loads, and the working capacity of supports and diaphragms.
However, the frequently installed lateral walls and braced frames subdivide the space and, thus, constrain architectural decisions. A rigid frame structure can span large openings and provide the design flexibility. Due to reversible direction of wind and seismic loads, the rigid frame elements, and particularly the field assembled girders and their moment-connected ends must be designed for both negative and positive bendings. (Assuming that the negative bending produces tension in the upper part of the girder and compression in the lower part, and positive bending acts in opposite directions.) A negative moment at a support, as a result of the horizontal and vertical loads, appears to be much bigger than a positive moment which is produced only by horizontal loads. The concrete girder and its end joints, proportioned to the worst loading condition, are complicated and cumbersome. The bending in a negative direction is a critical design consideration because of a lack of concrete in compression zones (especially in prestressed construction, where the lower portion of the girders already have been compressed by manufacturing). The composite action of a concrete plate located on the top of the girders is useless for negative moment restriction.
Accordingly, contrary to the preference of architectural designers, the lateral supports in known high rise buildings, which are heavily loaded by horizontal loads, are cumbersome and the distance between them is limited by the shear resistance offered by diaphragms and by the capacity of the supports.
Most commonly used floor and roof systems are used with a suspended ceiling. Such ceilings are necessary to hide the ribs or joists between adjacent precast slabs.
In part, the space above the suspended ceiling and below the associated slabs is used for pipes and conduits. The utilization efficiency of this space (like the efficiency of the extra space between horizontal levels of prefabricated modules, separately supported by beams) is usually low.
Among all the advantages of prefabricated building systems, there are two important difficulties as compared to poured concrete constructions. They are: (1) transportation of prefabricated elements and (2) obtaining the structural system integrity and stability. It is clear that the structural systems which are assembled from a plurality of separate members are more difficult to make stable and have the required integrity.
By increasing sizes of elements from large numbers of standard manufactured building parts to box-shaped, room-sized modules completely prefabricated in a shop, the time and labor required for assembling can be saved, but the expenses for transportation and erection will rise. But the total expenses can be minimized by using the optimum number of elements having optimum sizes.
The prior art includes the following U.S. Pat. Nos. 3,992,828; 3,712,008; 3,712,007; 3,638,380; 4,282,690; 4,341,051; 4,192,623; 4,186,535; 2,741,908; 3,110,982; 3,063,202; and 2,178,097.
It is an object of the present invention to provide an improved structural building system, comprised of prefabricated structural elements of optional unobstructive sizes, suitable for manufacturing, transportation, erection and assembling with a minimum of field labor and building construction time.
It is another object of the present invention to provide a relatively small number of different types of prefabricated building components, suitable for assembling a large number of various building designs and layouts.
It is a further object of the present invention to provide a stable prefabricated structural system by using rigid frames with composite girders and horizontal diaphragms accommodating precast floor slabs, which collectively act with a high degree of integrity.
It is a further object of the present invention to provide efficient load distribution by employing two-way slabs for floor elements and special frame connections which transmit bending moments in one direction only, providing positive bending of girders, appropriate for the properties and possibilities of reinforced concrete.
It is still another object of the present invention to replace the conventional cumbersome lateral supports by light rigid frames, providing big vertical apertures regardless of building height and loading conditions.
Another object of the present invention is to provide a composite girder, which employs the precast concrete floor slabs in composite action together with poured-in-place concrete and steel reinforcement.
A still further object of the present invention is to provide the high efficiency of the building space by using the room-size flat plates and eliminating wasted space between floor bearing construction and the suspended ceiling.
It is a further object of the present invention to eliminate the ceiling and to provide the utilization of the smooth underside of the floor slabs, which may be painted directly and left exposed for the ceiling.